Vol. XI · Flavour Plate 2 of 12five tastes, sweet, salty, sour, bitter, umami, threshold, intensity, Stevens law, concentrationF

The Five Tastes.

Quinine is bitter at three parts in a million; sugar needs four parts in a thousand to taste sweet. The tongue is built to notice poisons first.

Each of the five tastes has its own receptors on the tongue and palate. Sweet signals energy (sugars); salty, sodium the body needs; sour, acid — unripe fruit or spoilage; bitter, possible poisons; umami, the savoury taste of glutamate, a sign of protein (XI.5). Each has a threshold, the weakest concentration noticed, and they differ enormously: bitterness is noticed at concentrations thousands of times lower than sweetness.

Above the threshold, perceived intensity grows as a power of concentration (Stevens's law): roughly in proportion for salt and sugar, a little more steeply for sweetness, less steeply for sour and bitter. So doubling the sugar in a lemonade makes it a bit more than twice as sweet, and doubling the quinine makes a tonic noticeably but less than twice as bitter. The workshop maps all five.

Below: the perceived intensity of each taste against its concentration on logarithmic scales, with thresholds marked (teaching thresholds and exponents near the published ones), and the intensity of the taste and concentration you choose.

What you will learn

Name the five tastes and what they signal.
Compare their thresholds.
Use Stevens's law to predict intensity.
Adjust a taste by concentration.

Workshop

Intensity = (concentration ÷ threshold)^n, with thresholds (in % of the solution) sucrose 0.40, salt 0.06, citric acid 0.04, quinine 0.0003, MSG 0.02, and exponents 1.3, 1.3, 0.9, 0.8 and 1.0 (teaching values near those reported; individuals vary widely).

Thresholds and steepness

In these teaching values the threshold for sweetness is about 1,333 times that for bitterness: the tongue is far keener on possible poisons than on sugar. Doubling sugar from 5 % to 10 % makes a drink 2.46 times as sweet; doubling quinine makes a tonic only 1.74 times as bitter. A well-salted soup at 0.9 % salt sits about 34 times above the salt threshold on this scale.

Two cautions. Thresholds differ hugely between people: some taste a bitter compound that others cannot taste at all, and sensitivity changes with age, smoking and illness, so a dish that is right for one taster may not be for another. And the tastes interact: salt suppresses bitterness, sugar suppresses sourness, umami and salt enhance each other (XI.3–XI.6). Season by tasting, in small steps, at the temperature of serving.

At the stove

Make four glasses of water: one with a pinch of sugar, one with a pinch of salt, one with a squeeze of lemon, one with a little strong cold coffee. Dilute each by half, again and again, until you can no longer tell it from water. The coffee stays detectable longest.

Umami was named in 1908 by the Japanese chemist Kikunae Ikeda, who traced the savoury taste of kombu dashi to glutamate; its receptor was identified only in the 2000s, after which it was widely accepted as a fifth taste.

Terms

Threshold: The weakest concentration of a taste that is noticed.
Stevens's law: Perceived intensity grows as a power of stimulus strength.
Umami: The savoury taste of glutamate and certain nucleotides.
Bitter blockers: Compounds and tricks (salt, sugar, fat) that reduce perceived bitterness.

Each taste has a threshold and grows as a power of concentration; bitterness is noticed at far lower concentrations than sweetness.

Sources

S. S. Stevens, Psychophysics, Wiley, 1975: taste intensity grows as a power of concentration; exponents near 1.3 for sucrose and sodium chloride. The course uses teaching exponents near the published ones.
A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.